In the process of cell degeneration, platelets form in the bone marrow. These cells are responsible for the coagulation function of the blood and for the restoration of the walls of blood vessels.
Mature state
When speaking about the life expectancy of platelets, most specialists take into account only the period when they have already separated into a separate structure from the megakaryocyte. The period when they are only being formed and ripening is not taken into account.
On average, they are in the circulatory system for about a week. But the life span of human platelets can range from 5 to 12 days. Specialists distinguish several of their types: young, old, mature and forms of irritation. They depend not on the age of these cells, but on the characteristics of the hematopoiesis system.
Development cycle of
All platelets form in the bone marrow. Everything begins with a colony-forming megakaryocytic unit, it is also called "CFU-Meg".It shares mitosis. From it is formed first promegakarioblast, which turns into a megakaryoblast.
For 4-5 days in the bone marrow special cells - megakaryocytes, whose diameter is of the order of 60-120 microns are ripening. They are preceded by a special form with a non-grained basophilic cytoplasm and a tendency to polymorphism of the nucleus. It is called "promegakaryocyte".The ripe megakaryocyte is distinguished by the large dimensions of the cytoplasm and the presence of grains in it are violet-pink in color. The core in it is rough, it can be of various bizarre shapes.
It is from the cytoplasm of the megakaryocyte that small blood cells are separated, resembling discs in form. From this moment it is already possible to talk about the life expectancy of platelets. Evaluate, as a rule, only mature forms. They are in the body of a healthy person should be about 90%.
The number of
cells To understand why such a concentration of nuclear-free bodies is in the blood, one must know not only what the life span of platelets is, but also about how fast and how much they appear. For each kilogram of human weight, they are about 15x106.About 3,000 platelets are loosened from each megakaryocyte in the process of division. About 7-17% of the total is formed in the lungs. This is because prothrombocytes also enter the bloodstream. They independently reach the microcircular bed of the lungs. And already there is a process of platelet release.
Every day in the human body produces about 66 ± 14.6 thousand platelets per each μl of blood. In the blood of an adult, there should be between 180 and 320x109 of these blood cells; in children, they can range from 150 to 450x109.But when calculating their number, one must take into account age. For example, in newborns who have not yet reached 10 days, they can be from 99 to 420x109.
Appearance of
plates All mature corpuscles have the same structure. The life expectancy of platelets in the blood can vary. Each of disc-shaped plates does not contain a nucleus, but it has a centrally located granulomer, which consists of azurophilic grains. They can be from 5 to 20. Also, the mature platelets are distinguished by the lilac hyalomer and the presence of clear boundaries.
The diameter of the full cells is about 3-4 μm. They differ oval or round disk-like shape. Surface in a calm state is smooth. But when they come into contact with other bodies or an alien surface, threadlike processes immediately appear on the corpuscles, which give them a stellate shape.
Structure of
In addition to the information that the average life span of platelets is about 7 days, it is important to know that in each cell, three layers can be distinguished. The peripheral zone consists of an overmembrane zone, the purpose of which is to activate the platelet. Following it, there is a membrane responsible for adequate and timely reaction of the cell itself and clotting factors. It contains the so-called phospholipid matrix. It forms coagulation complexes. It is also responsible for the aggregation and adhesion of platelets.
In the sol-gel zone there are mitochondria. Also there pass special channels that connect this layer with the outer membrane. The sol-gel zone contains thrombosteine, which is responsible for the disk-like shape of the plates.
Separately experts allocate a site of organelles. It contains 4 types of granules. It is in them that the process of accumulation of coagulation factors takes place. They function throughout the entire time, regardless of the fact that the life span of the platelets is 5-12 days.
This division of the zones can be considered by repeatedly increasing the cells under a microscope.
Life cycle of platelets
After the blood platelets have separated from the megakaryocyte, they enter the bloodstream. It is worth noting that thrombopoietin is involved in the regulation of this process. It is necessary for the normal formation of platelets and the full maturation of the cytoplasm of megakaryocytes.
Approximately 1/3 of their total amount is deposited in the spleen. The remaining 70% circulate in the total blood flow. This depot is created in the spleen due to the fact that they move forward in this organ slowly enough. The process takes about 8 minutes. As a result, platelets are released into the total bloodstream and rush to the place where they are needed. All problems with the spleen are immediately displayed on the number of these blood plates. True, this does not affect the life span of platelets, but only changes their number in the blood. So, with its removal of the spleen, their concentration will be much higher. But with splenomegaly( an increase in this organ), these small cells move through it more slowly. This leads to a significant decrease in their amount in the blood.
It should be noted that only a small part of the platelets takes part in the processes of vascular reconstruction, tissue healing and blood clotting. The rest die in the bone marrow, spleen and liver under the influence of macrophages.